High tensile strength steel alloys



United States Patent 3,402,080 HIGH TENSILE STRENGTH STEEL ALLOYSHiroyuki Kubota and Junichi Tanaka, Kawasaki-ski, Japan, assignors toNippon Kokan Kabushiki Kaisha, Tokyo, Japan No Drawing. Filed Mar. 24,1966, Ser. No. 536,983 Claims priority, application Japan, Apr. 13,1965, 40/ 21,392 2 Claims. (Cl. 14836) ABSTRACT OF THE DISCLOSURE Thepresent invention relates to hardened and tempered steel alloys whichcontain relatively small amounts of vanadium and niobium and/ortitanium. These steel alloys have high tensile strength and can beproduced relatively cheaply and have a simpler composition than priorknown high tensile strength steel alloys.

Prior steel alloys having high tensile strength, for example, of theorder of from 70 to 80 kg./mm. are composed of very complicatedcompositions including very eX- pensive elements and or elements whichare very diflicult to add stably, such as nickel, molybdenum, boron andthe like so that it is necessary to prepare them with rni nute care. Bythis reason they are generally prepared by utilizing electric furnacesso that their cost of manufacture is extremely high.

This invention contemplates to obviate various difiiculties mentionedabove. When compared with conventional steel alloys having comparativestrength, steel alloys of this invention are advantageous in that theyare far cheaper and economic than prior alloys and especially that theycan be readily prepared, in some cases even by convertors since they donot contain any unstable element. As a result, preparation and field ofapplication of steel alloys having high tensile strength of the order offrom 70 to 80 kg./mm. are widened.

More particularly, the steel alloy of this invention is consisted offrom 0.10 to 0.2% of carbon, from 0.10 to 0.70% of silicon, from 1.00 to2.00% of manganese, from 0.10 to 0.50% of copper, from 0.10 to 0.70% ofchromium, from 0.01 to 0.20% of vanadium, from 0.01 to 0.10% of niobium,or titanium or both, and the balance of iron and impurities, said steelalloy being hardened and tempered to provide high tensile strength ofthe order of from 70 to 80 kg./mm.

The reason of adopting the above mentioned ranges of ingredients is asfollows: The lower limits for carbon and silicon correspond to theminimum values necessary for providing the required strength whiletherein upper limits correspond to the maximum values which are requiredso as not to impair the weldability of the steel alloy. The lower limitfor manganese is the value which is necessary to assure the requiredstrength, but the upper limit therefor corresponds to the maximum valueabove which the weldability is affected. Although incorporation ofcopper is effective to improve anticorrosion property and strength ofthe alloy but incorporation thereof above said upper limit causes rapiddecrease of hot workability. While chromium is a preferable element forincreasing anticorrosion property, according to this invention it isincorporated only when high strength is desired. Further vanadium is themost important element that contributes to increase the strength of thealloy steel, but stiffness and properties of the product are greatlyreduced with the increase in the quantity of incorporation of vanadium.By this reason, in prior steel alloys containing lesser quantity ofalloying ingredients it has been the practice to incorporate vanadium inexcess of about 0.1%. However in the 3,402,080 Patented Sept. 17, 1968"ice steel alloy embodying this invention inasmuch as the austenitegrains are rendered very fine, the impact property of the alloy steelhas been greatly improved so that it becomes possible'to incorporatevanadium of substantial quantity as mentioned above. As a result, it ispossible to produce alloy steels having high tensile strength of theorder of from 70 to 80 kg./mm. without impairing the stiffnessnotwithstanding their composition of low cost.

Table 1 below shows typical compositions of the high tensile strength ofsteel alloys of this invention containing lesser amount of alloyingingredients and examples of compositions of control samples, whereinsample members from A to M representing the novel steel alloys andsample members from O to T control samples not embodying this invention.

TABLE I.CHEMICAL COMPOSITIONS Chemical Composition (Percent) Sample No.

C Si Mn Cu Cr V Nb Ti The mechanical characteristics of various samplesshown in Table 1 is as shown in Table 2 below. In Table 2, the distancebetween marker points utilized to determine elongation was set to mm.,and E0 shows impact values at 0 C. obtained by using a 2 mm. V Charpyimpact test machine.

TABLE 2.MECHANICAL CHARACTERISTICS Sample Yielding Tensile Elonga-Reduc- E0,

No. point, strength, tion, tion, kg./cm.

kg./mm. kg./rnrn. percent percent As can be noted from the foregoingdescription this invention provides alloy steel of high tensile strengthof the order of from 70 to kg./mm. without using expensive nickel andmolybdenum, thus providing such high tensile strength steels at verycost. Further, since the alloy steels of this invention are not addedwith boron Which is unstable and has a tendency to harden them it isvery easy to prepare them. Further, the incorporation of vanadiumimproves the high temperature property while incorporation of niobium ortitanium assures sufiicient stiffness of the alloy steel. Moreover, thefact that the types 3 of elements incorporated are less and that noboron is incorporated makes it possible to produce steels of hightensile strength of the order mentioned above at low cost by converters.Thus the field of application of such high quality steels is greatlybroadened.

While there have been shown and described particular embodiments of theinvention, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the true spirit andscope of the invention as defined in the appended claims.

What is claimed is:

1. A hardened and tempered steel alloy of high tensile strength, saidalloy consisting essentially of about 0.10 to 0.20% of carbon, about0.10 to 0.70% of silicon,

about 1.00 to 2.00% of manganese, about 0.10 to 0.50% 5 of copper, about0.10 to 0.70% of chromium, about 0.10 to 0.20% of vanadium, about 0.01to 0.10% of both niobium and titanium, and the balance of iron andimpurities.

2. Alloy according to claim 1 wherein said alloy contains about 0.01 to0.10% of niobium only instead of both niobium and titanium.

References Cited UNITED STATES PATENTS 1,812,155 6/1931 Klinkenberg75-125 2,280,796 4/ 1942 Comstock 75-125 2,474,766 6/1949 Waggoner eta1. 75125 FOREIGN PATENTS 471,046 8/ 1937 Great Britain.

802,855 10/ 1958 Great Britain.

297,952 1932 Italy. 1,182,845 12/ 1964 Germany.

OTHER REFERENCES Welding Journal, vol. 33, No. 5, May 1954, pp. 251s-256$.

20 CHARLES N. LOVELL, Primary Examiner.

